1. Field of the Invention
The present invention relates to a process for the preparation of an ink for an ink jet printer. More particularly, the present invention relates to a process for the preparation of an ink which can be stably injected in a so-called drop-on-demand type ink jet printer. Such printers record information, e.g., by injecting ink particles by the action of a piezo-electric element, or by pressure created with bubbles formed by heating.
Description of the Related Art
In a recording head of a drop-on-demand type ink jet printer, ink particles are injected from a pressure chamber through a nozzle to a recording paper in accordance with an electric signal corresponding to information to be recorded. Usually, the recording head is driven by the action of a piezo-electric element provided at the pressure chamber, or by the action of a pressure of bubbles formed by heating a part of an ink in the pressure chamber (so-called bubble jet type).
It is known that, in an ink used for such an ink jet printer, a delay in the transfer of the pressure is caused by gas dissolved in the ink solvent and remaining therein, and the injection response characteristic is therefore degraded (see, for example, Japanese Examined Patent Publication (Kokoku) No. 53-20882 and Japanese Unexamined Patent Publication (Kokai) No. 55-17571). As means for obviating this disadvantage, there has been adopted, for example, a method in which, in the ink-preparing process, the dissolved gas is removed by heating the ink or by a reduction of the pressure therein, and during storage, the ink is contained and stored in a bag or pouch formed of a material having a low gas permeation coefficient, such as an aluminum-laminated film.
On the premise that if a large quantity of dissolved gas is present, the dissolved gas is released as bubbles by an abrupt change in the pressure at the time of the injection of the ink, and the injection response characteristic is thus reduced, we carried out ink injection tests using inks which had been subjected to the gas-removing treatment mentioned above and inks which had not been subjected to that gas-removing treatment. From the test results, we found that even if the dissolved gas remaining in the ink is removed by a reduction of the pressure or by heating, a stable injection could not be performed when a smaller size recording head was used. Nevertheless, it is thought that, to increase the recording speed, the size of the recording head must be reduced.
In Japanese Kokai No. 55-17571 and other publications, an ink jet printer provided with a super sonic vibration applying device is described. However, this device is still directed to remove, from an ink, gas bubbles dissolved in the ink during storage thereof or after the initial removal of gas bubbles by heating the ink or a reduction of the pressure therein. Therefore, a super sonic vibration applying device must be provided to an ink jet printer. Further, provision of a super sonic vibration applying device to an ink jet printer has disadvantages in that the construction of the printer becomes complicated and heating of the ink occurs.